Usage of state information from state-space based track-follow controller

ABSTRACT

A method according to one embodiment includes generating track following controller state information based on a positional signal of a head relative to a medium. One or more portions of the state information corresponding to particular frequencies are used to determine at least one of: lateral tape movement, tape skew, vibration operation conditions, and roller performance.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to using state information of atrack-follow controller for various purposes.

In magnetic storage systems, magnetic transducers read data from andwrite data onto magnetic recording media. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, the drive moves the magnetic tape over thesurface of the tape head at high speed. Usually the tape head isdesigned to minimize the spacing between the head and the tape. Thespacing between the magnetic head and the magnetic tape is crucial andso goals in these systems are to have the recording gaps of thetransducers, which are the source of the magnetic recording flux in nearcontact with the tape to effect writing sharp transitions, and to havethe read elements in near contact with the tape to provide effectivecoupling of the magnetic field from the tape to the read elements.

BRIEF SUMMARY

A method according to one embodiment includes generating track followingcontroller state information based on a positional signal of a headrelative to a medium. One or more portions of the state informationcorresponding to particular frequencies are used to determine at leastone of: lateral tape movement, tape skew, vibration operationconditions, and roller performance.

A system according to one embodiment includes a processor and logicintegrated with and/or executable by the processor. The logic isconfigured to generate track following controller state informationbased on a positional signal of a head relative to a medium. The logicis also configured to use one or more portions of the state informationcorresponding to particular frequencies to determine at least one of:lateral tape movement, tape skew, vibration operation conditions, androller performance.

A computer program product according to one embodiment includes acomputer readable storage medium having program instructions embodiedtherewith, the program instructions readable and/or executable by adevice to cause the device to perform the foregoing method.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a flowchart of a method according to one embodiment.

FIG. 4A is a graph illustrating a transfer function according to oneembodiment.

FIG. 4B is a matrix according to one embodiment.

FIG. 5A is an illustration of a transformation matrix according to oneembodiment.

FIG. 5B is an updated matrix according to one embodiment.

FIGS. 6A-6G are graphs depicting different representations according todifferent embodiments.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof. Various embodiments described herein include using stateinformation of a track-follow controller to recognize differentoperating conditions such as vibration and lateral tape movement, aswill be described in further detail below.

In one general embodiment, a method includes generating track followingcontroller state information based on a positional signal of a headrelative to a medium. One or more portions of the state informationcorresponding to particular frequencies are used to determine at leastone of: lateral tape movement, tape skew, vibration operationconditions, and roller performance.

In another general embodiment, a system includes a processor and logicintegrated with and/or executable by the processor. The logic isconfigured to generate track following controller state informationbased on a positional signal of a head relative to a medium. The logicis also configured to use one or more portions of the state informationcorresponding to particular frequencies to determine at least one of:lateral tape movement, tape skew, vibration operation conditions, androller performance.

In yet another general embodiment, a computer program product includes acomputer readable storage medium having program instructions embodiedtherewith, the program instructions readable and/or executable by adevice to cause the device to perform the foregoing method.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may operate under logicknown in the art, as well as any logic disclosed herein. The controller128 may be coupled to a memory 136 of any known type, which may storeinstructions executable by the controller 128. Moreover, the controller128 may be configured and/or programmable to perform or control some orall of the methodology presented herein. Thus, the controller may beconsidered configured to perform various operations by way of logicprogrammed into a chip; software, firmware, or other instructions beingavailable to a processor; etc. and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (integral or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, ROM device, etc., embedded into or coupled to theinside or outside of the tape cartridge 150. The nonvolatile memory isaccessible by the tape drive and the tape operating software (the driversoftware), and/or other device.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 3 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B made of the same orsimilar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 22 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2B depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2 and 2A-B together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complimentarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write transducer 214 and the readers, exemplified by the readtransducer 216, are aligned parallel to an intended direction of travelof a tape medium thereacross to form an R/W pair, exemplified by the R/Wpair 222. Note that the intended direction of tape travel is sometimesreferred to herein as the direction of tape travel, and such terms maybe used interchangeable. Such direction of tape travel may be inferredfrom the design of the system, e.g., by examining the guides; observingthe actual direction of tape travel relative to the reference point;etc. Moreover, in a system operable for bi-direction reading and/orwriting, the direction of tape travel in both directions is typicallyparallel and thus both directions may be considered equivalent to eachother.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (−), CZTor Al—Fe—Si (Sendust), a sensor 234 for sensing a data track on amagnetic medium, a second shield 238 typically of a nickel-iron alloy(e.g., ˜80/20 at % NiFe, also known as permalloy), first and secondwriter pole tips 228, 230, and a coil (not shown). The sensor may be ofany known type, including those based on MR, GMR, AMR, tunnelingmagnetoresistance (TMR), etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. However, different embodiments mayincorporate alternative orientations of the read and write transducers.For example, according to one approach, a R-W-R configuration may beimplemented. Moreover, in other approaches, an R-R-W configuration, aW-W-R configuration, etc. may be implemented with any of the embodimentsdescribed and/or suggested herein. In yet other variations, one or moreof the modules may have read/write pairs of transducers. Moreover, morethan three modules may be present. In further approaches, two outermodules may flank two or more inner modules, e.g., in a W-R-R-W, aR-W-W-R arrangement, etc. For simplicity, a W-R-W head is used primarilyherein to exemplify embodiments of the present invention. One skilled inthe art apprised with the teachings herein will appreciate howpermutations of the present invention would apply to configurationsother than a W-R-W configuration.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head may bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads.

As previously mentioned, the continued capacity scaling of tape systemshas led to increasing the track and linear bit density on recordingtape. However, as the track and linear bit densities on recording tapecontinue to be reduced, improvements to the precision of the positioningof the recording head over the data tracks is desired, e.g., to preventdata read and/or write errors. Furthermore, operation of tape drivesystems preferably includes robust performance of the track-follow servosystem under shock and vibration conditions. Particularly, the increasedtape track density lowers the tolerance in the acceptable trackfollowing error, thereby making it increasingly more challenging to meetthe performance specifications under vibration conditions.

Further still, computational delays created as a result of theimplementation of conventional track-follow controllers undesirablyreduce the performance of such conventional products, as real-timeinformation related to the system characteristics and operatingconditions is important in deriving and adjusting drive systemparameters related to the track-follow system. Specifically, controllerimplementations in conventional products are usually implemented in aseries of interconnected second-order sections. Although somewhatefficient in terms of the total computation time required, theseconventional products undesirably require that the output of thecontroller is calculated at the end of the computation of thesesecond-order systems. Therefore, the total computational time isincluded in the track-follow loop delay and affects the performance ofthe system as a whole. Specific examples of real-time information ofvarious system parameters are as follows.

A reliable estimation of lateral tape movement (LTM) is important forpositioning the coarse actuator at about the center of the LTM at thetarget track, as stack shifts create high amplitude tape displacement atlow frequencies that the fine actuator attempts to follow inconventional systems. In contrast, a reliable estimation LTM would allowfor the short-stroke, high-bandwidth fine actuator to follow the tapewithout the risk of running out of stroke. Yet, conventional controllerconfigurations rely on an LTM estimate which is provided by the outputof an integrator block. Moreover, for advanced controller designs ofsuch conventional controller configurations, e.g. H∞ controllers, theintegrator functionality is not implemented as a separate block but as apart of the overall controller.

Furthermore, skew-follow is highly desired in drives with flangelessrollers. In different embodiments, a tape skew estimate may enhance theskew-follow performance while also enabling reliable drive operation,e.g., in case only one servo channel is active. However, in conventionalproducts, an estimation of the tape skew requires a disturbance observerand additional computations, thereby increasing the delay and decreasingperformance of the system as a whole.

Additionally, determining the operation under vibration conditions maybe useful, e.g., in the case of switching controllers. For approacheswhich include switching controllers, a higher bandwidth track-followcontroller is selected when there is operation under vibrationconditions. However, conventional products rely on the amplitude of theposition error signal (PES) and/or the amplitude of the controlleroutput, which are misleading, especially in the case of a poorlyperforming drive. Several effects can increase the amplitude of PES orthe controller output and this may lead to an incorrect detection ofvibration conditions and thereby negatively affect the system.

Finally, some drives show poor performance in terms of PES due to poorroller quality. Determination of poor roller performance can be usefulduring manufacturing or roller characterization procedures. However,again conventional products are incapable of accessing and/or utilizingthis runtime information effectively.

Therefore, a new technique is desired for generating a reliableestimation of LTM, tape skew, vibration operating conditions and/or thepresence of poor roller performance drive. Preferably the foregoing areperformed in real time.

In sharp contrast to the shortcomings of conventional products describedabove, various embodiments described herein include a track-followcontroller implemented in a state-space form. The implementation instate-space form reduces the computational delay experienced in thetrack-follow loop of conventional products. Furthermore, a procedure isdescribed that explores the information provided by the states of thetrack-follow controller and provides important information in real timewithout significant additional computations, as will be described infurther detail below.

Looking now to FIG. 3, a method 300 is depicted in accordance with oneembodiment. As an option, the present method 300 may be implemented inconjunction with features from any other embodiment listed herein, suchas those described with reference to the other FIGS., such as FIG. 3. Ofcourse, however, such method 300 and others presented herein may be usedin various applications and/or in permutations which may or may not bespecifically described in the illustrative embodiments listed herein.Further, the method 300 presented herein may be used in any desiredenvironment. Thus FIG. 3 (and the other FIGS.) should be deemed toinclude any and all possible permutations.

Referring still to FIG. 3, method 300 includes generating trackfollowing controller state information based on a positional signal of ahead relative to a medium. See operation 302. According to one approach,the positional signal may be a PES, or signal derived therefrom.

Furthermore, operation 304 of method 300 includes using one or moreportions of the state information corresponding to particularfrequencies to determine at least one of: lateral tape movement, tapeskew, vibration operation conditions, and roller performance.

The condition determined may be output, stored, used for furtheroperations, etc. For example, upon determining at least one of theforegoing operation conditions, the corresponding data may be utilizedfor drive operations, e.g., controlling the coarse and/or fineactuators, controlling a skew actuator, altering a motor speed, etc. Seeoptional operation 306.

In preferred embodiments, the track following controller is implementedin state-space form. Accordingly, the state information may be generatedas a result of implementing a track-follow controller (e.g., of atrack-follow compensator) in state-space form, thereby reducing delaysof controllers and/or systems as a whole utilizing the stateinformation, particularly when compared to the shortcomings ofconventional products as previously mentioned.

As will be appreciated by one skilled in the art, a system having aninput and an output may be represented in state-space form. Moreover,the state-space representation of a given system may be achieved usingthe following equations, or equations known in the art.{circumflex over (x)}=Ax+Bu  Equation 1y=Cx+Du  Equation 2

Referring to the foregoing equations, x represents the state vector, urepresents the input vector and y represents the output vector.Additionally, A denotes a matrix having a size of n×n, where ‘n’ isdetermined by the number of states; B denotes a matrix having a size ofn×m, where ‘n’ is determined by the number of states and ‘m’ isdetermined by the number of inputs; C denotes a matrix having a size ofr×n, where ‘r’ is determined by the number of outputs and ‘n’ isdetermined by the number of states; and D denotes a matrix having a sizeof r×m, where ‘r’ is determined by the number of outputs and ‘m’ isdetermined by the number of inputs.

When applied to a track-follow controller, the input vector u isrepresented by the PES of the system of interest. In other words, theinput vector used in the state-space representation equations is the PESgenerated by a given tape drive, e.g., see 100 of FIG. 1A. Furthermore,the output vector y is preferably utilized for drive operations, e.g.,controlling the coarse, fine and/or skew actuators.

An exemplary in-use representation of how Equation 1 and Equation 2 maybe implemented in MATLAB for a given set of values, which are in no wayintended to limit the invention, is presented below.

A = x1 x2 x3 x4 x1 0.5929 0.4158 0.04852 0.07625 x2 −0.1805 0.4118−0.07221 0.03171 x3 −0.06018 −0.1498 0.9812 0.04232 x4 −0.00121−0.006091 0.00748 −0.0002513 B = u x1 0.1585 x2 0.07658 x3 0.09579 x4−0.0005478 C = x1 x2 x3 x4 y −300.8 1039 −124.5 3.045e+04 D = u y 159.4Sample time: 5e−05 seconds Discrete-time state-space model.

As shown, the resulting matrices are dependent on the number of states,inputs and outputs of the system being evaluated.

A microcode implementation of the foregoing in-use representation isalso presented below. It should be noted that, as previously mentioned,the input and output values of the below microcode implementation are inno way intended to limit the invention, but rather are presented by wayof example only.

y = Cx + Du y = Buffer + D(1,1) * u up = u X1p = X1 X2p = X2 X3p = X3X4p = X4 {dot over (x)} = Ax + Bu X1 = A(1,1) * X1p + A(1,2) * X2p +A(1,3) * X3p + A(1,4) * X4p + B(1,1) * up X2 = A(2,1) * X1p + A(2,2) *X2p + A(2,3) * X3p + A(2,4) * X4p + B(2,1) * up X3 = A(3,1) * X1p +A(3,2) * X2p + A(3,3) * X3p + A(3,4) * X4p + B(3,1) * up X4 = A(4,1) *X1p + A(4,2) * X2p + A(4,3) * X3p + A(4,4) * X4p + B(4,1) * up Cx Buffer= C(1,1) * X1 + C(1,2) * X2 + C(1,3) * X3 + C(1,4) * X4

According to additional embodiments, the resulting values of thestate-space representation for a given system may be presented inalternate configurations than those calculated in the foregoingexemplary in-use representations. For example, the state-spacerepresentation of a given track-follow controller may be simplified toproduce a block-diagonal matrix. According to some approaches, ablock-diagonal matrix may have a block size of 1×1 for real eigenvalues,and a block size of 2×2 for complex eigenvalues.

An exemplary in-use representation of how Equation 1 and Equation 2 maybe implemented in MATLAB for a given set of values to produce asimplified state-space representation, which again are in no wayintended to limit the invention, is presented below.

A = x1 x2 x3 x4 x1 0.4929 0.2606 0 0 x2 −0.2606 0.4929 0 0 x3 0 0 1 0 x40 0 0 1.549e−17 B = u x1 −30.77 x2 −61.02 x3 9 x4 0.003378 C = x1 x2 x3x4 y 2.601 −1.359 0.02214 59.19 D = u y 159.4 Sample time: 5e−05 secondsDiscrete-time state-space model.

As shown, the resulting A matrix includes several ‘0’ values whichultimately simplifies the calculations required to produce the remainderof the data used to produce the state-space representation.

Furthermore, a microcode implementation of the foregoing in-userepresentation is also presented below. It should be noted that, aspreviously mentioned, the input and output values of the below microcodeimplementation are in no way intended to limit the invention, but ratherare presented by way of example only.

y = Buffer + D(1,1) * u y = Cx + Du up = u X1p = X1 X2p = X2 X3p = X3X4p = X4 X1 = A(1,1) * X1p + A(1,2) * X2p + {dot over (x)} = Ax + Bu 0 +0 + B(1,1) * up X2 = A(2,1) * X1p + A(2,2) * X2p + 0 + 0 + B(2,1) * upX3 = 0 + 0 + A(3,3) * X3p + 0 + B(3,1) * up X4 = 0 + 0 + 0 + A(4,4) *X4p + B(4,1) * up Buffer = C(1,1) * X1 + C(1,2) * X2 + Cx C(1,3) * X3 +C(1,4) * X4

However, it should also be noted that for embodiments having repeatedeigenvalues and/or clusters of nearby eigenvalues, the block size may belarger than those seen in the exemplary representations above. Forexample, a model of the A matrix for a system having eigenvalues of(λ₁,σ±jω,λ₂) is presented below.

$\quad\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \sigma & \omega & 0 \\0 & {- \omega} & \sigma & 0 \\0 & 0 & 0 & \lambda_{2}\end{bmatrix}$

When implementing the foregoing state-space representation to atrack-follow controller, the corresponding PES is used in Equation 1 andEquation 2 as the input vector u. FIGS. 4A-4B illustrate a graph 400 anda corresponding A matrix 450, respectively. A matrix 450 was producedusing one or more of the foregoing processes, e.g., using Equation 1 andEquation 2. Moreover, it should be noted that the graph 400 and acorresponding A matrix 450 correspond to an exemplary track-followcontroller which is in no way intended to limit the invention, butrather is presented by way of example only.

Looking to FIGS. 4A-4B, the eigenvalues of matrix 450 correspond tospecific frequency ranges of the graph 400 of the track-followcontroller. Accordingly, the different eigenvalues of matrix 450 andmatching frequency ranges of the graph 400 are marked with callouts.

Referring still to FIGS. 4A-4B, the inventors found that the eigenvaluesof matrix 450 correspond to frequency ranges of interest on the graph400. Specifically, for the lower frequencies of graph 400 having twointegrators running, they correspond to the portion of matrix 450labeled with 0.3 Hz. Furthermore, the slight bulge at about 90 Hzcorresponds to the eigenvalues of matrix 450 labeled 90 Hz whichrepresents an area where the track-follow controller had a higher gainas a result of an enhanced disturbance rejection to accommodate forgiven vibration environments. Further still, the three peaks seen ingraph 400 correspond to the three roller frequencies of the track-followcontroller and are represented by callouts 150 Hz, 300 Hz and 450 Hz. Itfollows that each line of the matrix actually corresponds to a state ofa track-follow controller.

Furthermore, a transformation matrix may be applied to matrix 450 toorder the state coordinates and ensure a fixed location of theeigenvalues within the matrix. Moreover, by applying transformationmatrix 500 as illustrated in FIG. 5A, the eigenvalues of matrix 450 maybe reordered such that they are arranged in numerical order based on thefrequency range of the graph 400 to which they correspond as illustratedin the matrix 550 FIG. 5B.

Referring back to the method 300 of FIG. 3, once the track followingcontroller state information is generated, one or more portions of thatstate information corresponding to particular frequencies may be used todetermine one or more of: LTM, tape skew, vibration operationconditions, and roller performance. Specifically, according to preferredembodiments, the eigenvalues of an updated matrix (e.g., 550 of FIG. 5B)corresponding to the controller state information of a track-followcontroller may be useful, for determining drive operation(s), in thefollowing cases. It should be noted that although matrix 550 of FIG. 5Bis used in the following descriptions, this is done by way of exampleonly and is in no way intended to limit the invention. In otherembodiments, matrices having different values and corresponding todifferent track-follow controllers may be used to determine one or moreof the LTM, tape skew, vibration operation conditions, and rollerperformance for a given system. Furthermore, it should also be notedthat according to other embodiments, eigenvalues corresponding toparticular states of the system may be positioned differently among therows and/or columns than as shown in matrix 550.

In view of the foregoing statement, the lateral tape movement may bedetermined using the one or more portions of the state information whichcorrespond to one or more if the values presented in the eigenvalues ofrows 13 (i.e., X13) and 14 (i.e., X14) in matrix 550. Momentarilyreferring to graph 600 of FIG. 6A, stack shifts create high amplitudetape displacement at low frequencies as illustrated by the controlleroutput. In many cases, for conventional products the fine actuator isfaced with compensating for these stack shifts which results in errorsdue to the fine actuator's low stroke as well as the slow computing timeand unreliable LTM calculations produced by such conventional products.

Conversely, embodiments presented herein may produce a reliable LTMestimation using the following equation, or an equation known in theart.LTM_(EST) =−C(1,13)*X13−C(1,14)*X14  Equation 3

As shown, Equation 3 uses the frequency integrator states correspondingto the values presented in the eigenvalue of rows 13 and 14 in matrix550 (FIG. 5B) to generate a reliable LTM estimate which may be used toposition the coarse actuator at about the center of the LTM, e.g., at atarget track. By using the coarse actuator to compensate for stackshifts of the LTM, this allows for the short stroke, high bandwidth fineactuator to follow the tape without the risk of running out of stroke.

In other words, the lateral tape movement may be determined using theone or more portions of the state information which correspond to thelower frequency characteristics of the controller in general. Morespecifically, the lateral tape movement may be determined using the oneor more portions of the state information which correspond to one ormore lower frequency portions of the state information relative to thoseusable for determining at least one of the vibration operationconditions and roller performance, as will soon become apparent. Thoseskilled in the art, once armed with the teachings herein, would be ableto determine via routine experimentation which portions of stateinformation of a give system would be usable for determining the variousoperating conditions mentioned herein.

Referring again to matrix 550 of FIG. 5B, an estimation of tape skew maybe derived from a low frequency double integrator state. According to apreferred approach, one or more portions of the state information whichcorrespond to one or more if the values presented in the eigenvaluepresented in row 14 (i.e., X14) of matrix 550 may be used fordetermining the tape skew.

The ability to generate a reliable estimation of tape skew, e.g., toimplement in a drive, is of significant desirability for systems havingflangeless rollers as would be appreciated by one skilled in the art. Areliable estimation of tape skew can, among other things, enhanceskew-follow performance, enable reliable drive operation even if onlyone servo channel is active, and improve the performance of theskew-follow control system.

According to a preferred embodiment, which again is in no way intendedto limit the invention, a scaled value of the tape skew for a givensystem may be estimated using the following equation, or an equationknown in the art.SKEW_(EST) =−C(1,14)*X14  Equation 4

By implementing the foregoing equation, the skew estimate simplifies theimplementation of the skew control scheme seeing that as a result,neither a disturbance observer nor additional computations are required.Moreover, a reliable and accurate estimation of tape skew is achievablefor embodiments regardless of whether they have open loops and/or closedloops, as shown in graphs 610, 620 of FIGS. 6B-6C, respectively.Conventional systems are incapable of accurately estimating tape skew inclosed loop systems without the use of additional structures (e.g.disturbance observer).

Thus, the tape skew may be determined using the one or more portions ofthe state information which correspond to one or more lower frequencyportions of the state information relative to those usable fordetermining at least one of the vibration operation conditions androller performance, as will soon become apparent.

According to additional embodiments, vibration operation conditions mayalso be determined using one or more portions of the state informationwhich correspond to one or more if the values presented in theeigenvalues of rows 11 (X11)and 12 (i.e., X12), e.g., as presented inmatrix 550 of FIG. 5B.

Some approaches may implement a threshold value to determine thepresence of vibration operation conditions. For example, if the value ofVIB_(INFO) is greater than a given threshold, it may be presumed thatvibration conditions are not present, while if the value of VIB_(INFO)is less than a given threshold, it may be presumed that vibrationconditions are present. Depending on the desired approach, the thresholdmay be predetermined, set by a user, calculated based on stateinformation, etc. Moreover, in some approaches, determining vibrationoperation conditions may be useful when switching controllers of a givensystem.VIB_(INFO) =−C(1,11)*X11−C(1,12)*X12  Equation 5

Using Equation 5 is greatly preferred over alternative options,particularly attempts to compare the PES and the controller output of agiven system as this alternative method is highly misleading. Theamplitude of the PES and controller output of a given system are similarand difficult to distinguish between, especially for systems having poorperformance drives. Such complications may lead to an incorrectdetection of vibration conditions, thereby compromising the performanceof the system as a whole. In sharp contrast, looking to graph 630 ofFIG. 6D, a noticeable difference in amplitude separates the controllerstate information with vibrations from that without vibrations.

In other words, the vibration operation conditions may be determinedusing the one or more portions of the state information which correspondto one or more lower frequency portions of the state informationrelative to those usable for determining the roller performance andhigher than those usable for at least one of the lateral tape movementand the tape skew, as will soon become apparent. However, in alternativeapproaches, the vibration operation conditions may be determined usingthe drive vibration specification as would be appreciated by one havingordinary skill in the art upon having read the present description.

Further still, alternate embodiments may be able to determine thepresence of poor roller performance drives using state informationresponsible for roller frequency disturbance rejection. Thus, someembodiments may be able to determine the roller performance using thevalues presented in the eigenvalues of rows 9 (i.e., X9) and 10 (i,e.,X10); 7 (i.e., X7) and 8 (i.e., X8); and 5 (i.e., X5) and 6 (i.e., X6);e.g., as presented in matrix 550 of FIG. 5B.

Some drives have undesirable performance in terms of PES as a result ofpoor roller quality, as would be appreciated by one skilled in the art.Thus, determination of poor roller performance is desirable. Accordingto some embodiments, monitoring the state information corresponding toroller frequency disturbance rejections provides an option to determinepoor roller performance. Specifically, one or more of the followingequations, and/or equations known in the art, may be used to performmonitoring of the roller performance, e.g., depending on the desiredembodiment, performance conditions, tolerance factors, etc.R _(F1) =−C(1,9)*X9−C(1,10)*X10  Equation 6R _(F2) =−C(1,7)*X7−C(1,8)*X8  Equation 7R _(F3) =−C(1,5)*X5−C(1,6)*X6  Equation 8

As illustrated in FIGS. 6E-6G, exemplary results of implementingEquations 6-8 respectively are presented. It should be noted that thedata in each of the graphs 640, 650, 660 of FIGS. 6E-6G is presented byway of example and is in no way intended to limit the invention.

It follows that, in view of the foregoing description, the rollerperformance may be determined using the one or more portions of thestate information which correspond to one or more higher frequencyportions of the state information relative to those usable fordetermining at least one of the vibration operation conditions, thelateral tape movement, and the tape skew.

Moreover, this roller performance information may be used to determinethe drive performance, at least in part. Whether or not a drive has poorperformance in terms of PES because of poor roller quality cannot bedetermined by simply looking at the corresponding PES, but rather ifstates associated with the roller performance characteristic of thedrive are monitored, poor performances may be identified if it is causedby the rollers. For example, looking to graphs 640, 650, 660, there aresome poorly performing rollers in addition to some rollers that areperforming well. It becomes apparent that higher values correspond topoor roller performance issues, while lower values on the graphs areassociated with better roller performance. Thus, by monitoring thisdata, the roller performance may be determined.

According to some approaches, one or more of the frequencies of rollerdisturbances for a given embodiment may be calculated based at least inpart on the roller rotation frequency, e.g., by using the followingequation:f=v/(πR)  Equation 9Looking to the variables of Equation 9, v represents the tape speedwhile R represents the radius of the roller. Once the roller rotationfrequency f has been calculated, multiples of the frequency value may beused to capture the multiple harmonics of a given embodiment.Furthermore, it should be noted that for roller disturbances, thefrequency of the roller rotation varies with the operating tapevelocity; however a frequency corresponding to a vibration disturbancedoes not varying given different operational velocities of tape.

According to some embodiments, one or more threshold values may be usedto distinguish when a drive has poor roller performance. For example, itmay be determined that a drive has poor roller performance if the resultof any one or more of Equations 6-8 result in a value that is above agiven threshold, while a drive may have a good or acceptable rollerperformance if the result of any one or more of Equations 6-8 result ina value that is below a given threshold. As described above, a thresholdmay be predetermined, set by a user, calculated based on stateinformation, etc.

As described above, upon determining at least one of the foregoingoperation conditions, the corresponding data may be output, stored,utilized for drive operations, e.g., controlling the coarse and/or fineactuators (e.g., see 132 of FIG. 1A), etc. As a result, by implementingthe track-follow controller in state-space form, various embodimentsdescribed and/or suggested herein are able to reduce the effects ofcomputational delay. Moreover, utilizing the track following controllerstate information allows for the generation of important systeminformation in real time, i.e., without added computational delays.

When compared to conventional methods of calculating each of theforegoing system characteristics, the various embodiments describedherein greatly improve overall performance by reducing delays of thecontroller (e.g., 128 of FIG. 1A) and/or the system as a whole.

Although many embodiments described above implement the state-spacerepresentation of a track-follow controller, similar results may beachieved for embodiments applying a transfer function representation ofa track-follow controller. According to one approach, the followingequation, or an equation known in the art, may be used to generate arepresentation of a given track-follow controller.

$\begin{matrix}{{K(s)} = {\frac{B(s)}{A(s)} = \frac{{b_{1}s^{n - 1}} + \ldots + {b_{n - 1}s} + b_{n}}{{a_{1}s^{m - 1}} + \ldots + {a_{m - 1}s} + a_{m}}}} & {{Equation}\mspace{14mu} 9}\end{matrix}$

Moreover, in some approaches, Equation 9 may additionally oralternatively be used to form a graphical representation of atrack-follow controller, e.g., as seen in graph 400 of FIG. 4A.

It should also be noted that any of the operations of method 300 and/orany embodiments associated therewith described and/or suggested hereinmay be performed by a processor of a system, such as a controller (e.g.,see 128 of FIG. 1A).

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), etc. By executable by the processor, what is meant is that thelogic is hardware logic; software logic such as firmware, part of anoperating system, part of an application program; etc., or somecombination of hardware and software logic that is accessible by theprocessor and configured to cause the processor to perform somefunctionality upon execution by the processor. Software logic may bestored on local and/or remote memory of any memory type, as known in theart. Any processor known in the art may be used, such as a softwareprocessor module and/or a hardware processor such as an ASIC, a FPGA, acentral processing unit (CPU), an integrated circuit (IC), a graphicsprocessing unit (GPU), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A method, comprising: generating track followingcontroller state information based on a positional signal of a headrelative to a medium; using one or more portions of the stateinformation corresponding to particular frequencies to determine atleast one of: vibration operation conditions of a drive environment,wherein the one or more portions of the state information used fordetermining the vibration operation conditions correspond to one or morelower frequency portions of the state information relative to thoseportions of the state information usable for determining rollerperformance and higher than those portions of the state informationusable for at least one of lateral tape movement and tape skew; androller performance, wherein the one or more portions of the stateinformation used for determining the roller performance correspond toone or more higher frequency portions of the state information relativeto those portions of the state information usable for determining atleast one of the vibration operation conditions, the lateral tapemovement, and the tape skew.
 2. A method as recited in claim 1,comprising determining lateral tape movement using the one or moreportions of the state information.
 3. A method as recited in claim 2,wherein the one or more portions of the state information used fordetermining the lateral tape movement correspond to one or more lowerfrequency portions of the state information relative to those portionsof the state information usable for determining at least one of thevibration operation conditions and roller performance, wherein the stateinformation is also used to control a fine actuator during read andwrite operations.
 4. A method as recited in claim 1, comprisingdetermining tape skew using the one or more portions of the stateinformation.
 5. A method as recited in claim 4, wherein the one or moreportions of the state information used for determining the tape skewcorrespond to one or more lower frequency portions of the stateinformation relative to those portions of the state information usablefor determining at least one of the vibration operation conditions androller performance.
 6. A method as recited in claim 1, wherein the atleast one of the vibration operation conditions and the rollerperformance that is determined includes the vibration operationconditions.
 7. A method as recited in claim 1, wherein the at least oneof the vibration operation conditions and the roller performance that isdetermined includes the roller performance.
 8. A method as recited inclaim 1, wherein the state information is implemented in state-spaceform, wherein the one or more portions of the state information areeigenvalues of a matrix corresponding to the controller stateinformation of a track-follow controller.
 9. A system, comprising: aprocessor and logic integrated with and/or executable by the processor,the logic being configured to: generate track following controller stateinformation based on a positional signal of a head relative to a medium;use one or more portions of the state information corresponding toparticular frequencies to determine at least one of: lateral tapemovement, wherein the lateral tape movement is used to position a coarseactuator at about a center position between outer extents of the lateraltape movement in response to determining the lateral tape movement, tapeskew, vibration operation conditions of a drive environment, and rollerperformance, wherein the state information is implemented in state-spaceform, wherein the one or more portions of the state information areeigenvalues of a matrix corresponding to the controller stateinformation of a track-follow controller.
 10. A system as recited inclaim 9, wherein the at least one of the lateral tape movement, tapeskew, vibration operation conditions and the roller performance that isdetermined includes the lateral tape movement.
 11. A system as recitedin claim 9, wherein the at least one of the lateral tape movement, tapeskew, vibration operation conditions and the roller performance that isdetermined includes the tape skew.
 12. A system as recited in claim 9,wherein the at least one of the lateral tape movement, tape skew,vibration operation conditions and the roller performance that isdetermined includes the vibration operation conditions.
 13. A system asrecited in claim 9, wherein the at least one of the lateral tapemovement, tape skew, vibration operation conditions and the rollerperformance that is determined includes the roller performance.
 14. Asystem as recited in claim 9, further comprising: a drive mechanism forpassing a magnetic medium over a magnetic head; and a controllerelectrically coupled to the magnetic head.
 15. A computer programproduct comprising a computer readable storage medium having programinstructions embodied therewith, the program instructions readableand/or executable by a controller to cause the controller to: generate,by the controller, track following controller state information based ona positional signal of a head relative to a medium; and use, by thecontroller, one or more portions of the state information correspondingto particular frequencies to determine roller performance, wherein theroller performance is determined using the one or more portions of thestate information, wherein the one or more portions of the stateinformation correspond to roller frequency disturbance rejections. 16.The computer program product of claim 15, wherein lateral tape movementis determined using the one or more portions of the state information,wherein tape skew is determined using the one or more portions of thestate information, wherein vibration operation conditions is determinedusing the one or more portions of the state information, wherein theroller performance is determined using the portions of the stateinformation.